1. Field of the Invention
The present invention relates to a service life indicator for a process cartridge which is used for image formation and which contains therein at least one consumable, the process cartridge being detachably mountable into a main assembly or body of the image forming apparatus.
2. Description of the Prior Art
The prior art will be described with respect to an electrophotographic copying apparatus, as an example of the image forming apparatus.
Conventionally, electrophotographic machines require a trained and expert serviceman for replacement of the photosensitive member, which is an image bearing member, supply of the developer, disposal of used developer, cleaning of charging wires, replenishment and adjustment of various parts and so on. It is required that the serviceman go to offices having the electrophotographic machines whenever servicing is necessary. This is disadvantageous both for machine makers and machine users, since the makers have to establish and maintain a servicing network to meet the demand for service, and the users have to wait for the serviceman to arrive and then fix the machine before the restart of the machine operation.
Those problems are relatively less serious in the case of large or middle size copying machines, since the number of such copying machines installed is not so large. However, in the case of machines for personal use, the problem is more serious, since the number of machines which are being used is very large, and also since the degree of use is very diffierent among them. Maintenance will be practically very difficult in those cases.
To remove those disadvantages, it is recently proposed, as disclosed in U.S. Pat. No. 3985436, that various process means, such as the photosensitive member, developing device, cleaning means and charger are all contained in a casing as a unit, and that the unit is replaced with a fresh unit when the service life of the photosensitive member ends, so that all the means contained therein are exchanged simultaneously, thus eliminating the machine servicing operation. This makes it possible for users to replace various elements without resort to an expert serviceman and eliminates the necessity of periodic maintenance.
That is, the replacement of the unit (hereinafter also called "process cartridge") covers the replacement of the worn-out photosensitive member, the supply of the developer, the disposal of used developer, the cleaning of a corona discharging wire stained by the developer, for example, and the cleaning of the developing device.
The problems of users can be solved by this approach, since the various process means requiring periodic and/or occasional servicing operations can be replaced with fresh ones simply by replacement of the process cartridge.
It is possible to prepare various process cartridges having different developing characteristics and different reproducing characteristics, and for a user to keep several on hand and use one depending on the desired characteristics. Therefore, there are more opportunity for taking and keeping the process cartridges out of the machine to use another type cartridge or for some maintenance, during the service life of the process cartridge.
Since supply or replacement of consumables is carried out by servicing operators in conventional devices, the degree of use of the machine is known by the servicing operators by checking the counter or the like provided in the machine. Where, however, plural types of the cartridges are interchanged in use by the users themselves, a counter provided on the side of the main assembly can not give the correct usage for the respective cartridges.